Hypersound Attenuation in Superconductors by Quasiparticle Creation

Abstract

The attenuation of 10-GHz longitudinal sound waves in superconducting molybdenum ($T_c=0.914\mathrm{}$ K) and cadmium ($T_c=0.500\mathrm{}$ K) shows the high-frequency behavior predicted by the BCS theory. In particular, the onset of the rapid drop in attenuation with decreasing temperature that is characteristic of superconductors is shifted downward to the temperature $T_{\nu }$ (0.905 K in molybdenum and 0.490 K in cadmium) at which the superconducting energy gap equals the phonon energy. The analysis of the measurements indicates a large anisotropy in the energy gaps of both metals.